Compressor and refrigerating cycle apparatus using the same

ABSTRACT

In a compressor, a single refrigerant of hydrofluoroolefin having a double bond of carbon or a mixed refrigerant containing hydrofluoroolefin and hydrofluorocarbon having no double bond of carbon is used, and moreover a refrigerating machine oil containing an additive for suppressing deterioration of the refrigerating machine oil and an antiwear agent is used, the compressor including a sliding portion which is exposed to the mixed refrigerant and the refrigerating machine oil and which has a hardness of 47-55 HRC. Thus, decomposition and polymerization of the refrigerant and the refrigerating machine oil can be inhibited (i.e., occurrence of sludge can be inhibited), and antiwear property of sliding portions, e.g. vane and piston, of the compressor can be maintained. As a result, reliability of the compressor and the refrigerating cycle apparatus using the compressor can be ensured.

TECHNICAL FIELD

The present invention relates to a compressor, and a refrigerating cycle apparatus, using a refrigerant having a lower global warming potential and composed principally of a hydrofluoroolefin having a double bond of carbon.

BACKGROUND ART

Refrigerants to be used for compressors and for refrigerating cycle apparatuses using compressors have been moving to HFC (hydrofluorocarbon) series having an ozone depletion potential of 0 (hereinafter, referred to as HFC refrigerants).

A compressor, and a refrigerating cycle apparatus, using an HFC refrigerant will be explained with reference to FIGS. 7 to 9 (see, e.g., PTLs 1 and 2).

FIG. 7 is a longitudinal sectional view of a rotary compressor using an HFC refrigerant described in PTL 1.

A stator 2 a of a motor 2 is fixed at an upper portion of a closed container 1. A compression mechanism section 5 having a shaft 4 driven by a rotor 2 b of the motor 2 is fixed at a lower portion of the closed container 1. A bearing 7 is fixed at an upper end of a cylinder 6 of the compression mechanism section 5 with a bolt or the like while a bearing 8 is fixed at a lower end of the cylinder 6 with a bolt or the like. A piston 9 is placed in the cylinder 6. An eccentric portion 4 a of the shaft 4 is inserted into the piston 9, and the piston 9 is eccentrically rotated by the eccentric portion 4 a.

Within the closed container 1, an R410A (a mixture of HFC32 and HFC125) is enclosed as a refrigerant. Stored at a bottom portion of the closed container 1 is refrigerating machine oil 103 having polarity and being compatible with the refrigerant, such as polyol ester (POE) or polyvinyl ether (PVE).

FIG. 8 is a cross-sectional view of a rotary compressor using an HFC refrigerant described in PTL 1. A space between the cylinder 6 and the piston 9 is divided by a vane 10, thereby forming a suction chamber 13 into which the refrigerant is sucked up and a compression chamber 14 in which the refrigerant is compressed.

A rotary compressor constructed as described above will be described in terms of operation and function.

First, the refrigerant is sucked into the suction chamber 13 via a suction port 12 provided in the cylinder 6. Also, the refrigerant in the compression chamber 14 is compressed by counterclockwise rotation (arrow direction) of the piston 9, and passes through a discharge cutout 15 so as to be discharged into the closed container 1 via a discharge port (not shown). The compressed refrigerant discharged into the closed container 1 passes through an opening of the motor 2 so as to be discharged outside the closed container 1 via a discharge pipe 16 placed at an upper portion of the closed container 1. In this process, mist of the refrigerating machine oil 103 present in vicinities is also discharged out together.

Next, a basic refrigerating cycle apparatus having a rotary compressor 20 for sucking up and compressing an HFC refrigerant and discharging out the refrigerant, as described in PTL 2, will be described with reference to FIG. 9.

As shown in FIG. 9, the rotary compressor 20 compresses a low-temperature, low-pressure refrigerant gas and discharges out a high-temperature, high-pressure refrigerant gas toward a condenser 21. The HFC refrigerant gas fed to the condenser 21 has its heat released into the air, resulting in a high-temperature, high-pressure refrigerant liquid and being fed to an expansion mechanism (e.g., expansion valve or capillary tube) 22. The high-temperature, high-pressure refrigerant liquid passing through the expansion mechanism 22 becomes a low-temperature, low-pressure wet steam by a restriction effect, being fed to an evaporator 23. The refrigerant having entered into the evaporator 23 absorbs heat from vicinities so as to evaporate. The low-temperature, low-pressure refrigerant gas having come out of the evaporator 23 is sucked into the rotary compressor 20. Such a cycle as shown above is repeated.

HFC refrigerants mentioned above, which are hard to decompose in atmospheric air and very high in global warming potential (hereinafter, referred to as GWP), have been becoming an issue from the viewpoint of global environment protection. Thus, there have been being made discussions upon refrigerants being lower in GWP and composed principally of hydrofluoroolefin having a double bond of carbon.

CITATION LIST Patent Literature

PTL 1: JP H11-236890 A

PTL 2: JP H8-240362 A

SUMMARY OF INVENTION Technical Problem

However, refrigerants composed principally of hydrofluoroolefin having a double bond of carbon, which are indeed low in GWP, yet are more liable to decompose as compared with HFC refrigerants, having difficulty in stability.

Therefore, for example, heat generated at sliding portions of the rotary compressor such as a tip end portion 10 a of the vane 10 of the compressor and an outer peripheral surface of the piston 9, causes occurrence of decomposition and polymerization of the refrigerant and the refrigerating machine oil, so that sludge may be generated. This sludge may cause faults of the rotary compressor as well as sludge clogging within the refrigerating cycle apparatus.

This being the case, the inventor added an antioxidant and the like to the refrigerating machine oil so as to inhibit occurrence of reaction products of the refrigerant. As a result, it proved that decomposition of the refrigerant is inhibited and occurrence of fluorine compounds contained in the reaction products is also inhibited. The fluoric compounds have been confirmed to enhance the wear resistance property when sucked up to sliding portions between the tip end portion of the vane and the outer peripheral surface of the piston and the like. Therefore, inhibition of the generation of such fluoric compounds may cause progress of wear of the sliding portions, making it impossible in some cases to maintain the reliability of the compressor, i.e. of the refrigerating cycle apparatus using the compressor.

As a solution to this, the inventor conceived to add an antiwear agent such as extreme-pressure additive to the refrigerating machine oil. However, through various experiments, the inventor found that with use of a refrigerant having a double bond of carbon and composed principally of hydrofluoroolefin, an antiwear effect cannot securely be obtained only by adding an antiwear agent to the refrigerating machine oil. Therefore, it is an important issue that the effect of the antiwear agent is enhanced to maintain the reliability of the compressor, i.e., refrigerating cycle apparatus.

Accordingly, it is an object of the present invention to provide a high-reliability compressor, as well as a refrigerating cycle apparatus using the compressor, capable of inhibiting decomposition and polymerization of the refrigerant and the refrigerating machine oil to thereby inhibit occurrence of sludge by and moreover maintain wear-resistant property of the compressor.

Solution to Problem

In order to achieve the above object, the present invention has the following constitutions.

In one aspect of the invention, there is provided a compressor for use in a refrigerating cycle apparatus, wherein a single refrigerant of hydrofluoroolefin having a double bond of carbon or a mixed refrigerant containing the hydrofluoroolefin and hydrofluorocarbon having no double bond of carbon is used, and a refrigerating machine oil containing an additive for suppressing deterioration of the refrigerating machine oil and an antiwear agent is used, the compressor including a sliding portion which is exposed to the mixed refrigerant and the refrigerating machine oil and which has a hardness of 47-55 HRC.

In another aspect of the invention, there is provided a refrigerating cycle apparatus comprising: the compressor as mentioned above; a condenser; an expansion mechanism; and an evaporator, whereby a refrigerating cycle for compressing, condensing, expanding and evaporating the refrigerant is constituted.

Advantageous Effects of Invention

According to the present invention, decomposition and polymerization of the refrigerant and the refrigerating machine oil is inhibited, so that occurrence of sludge is inhibited. Also, antiwear property of sliding portions, e.g. vane and piston, of the compressor can be maintained. As a result, reliability of the compressor and the refrigerating cycle apparatus using the compressor can be ensured.

BRIEF DESCRIPTION OF DRAWINGS

The above aspects and features of the present invention will become more apparent from the following description of preferred embodiments thereof with reference to the accompanying drawings, and wherein:

FIG. 1 is a configuration view of a refrigerating cycle apparatus according to an embodiment of the present invention;

FIG. 2 is a longitudinal sectional view of a rotary compressor according to an embodiment;

FIG. 3 is a cross-sectional view of the rotary compressor according to an embodiment;

FIG. 4 is a chart showing characteristic correlations among operating time, wear quantity of the piston and total acid number of the refrigerating machine oil with respect to each of different refrigerating machine oils according to an embodiment;

FIG. 5 is a chart showing characteristic correlations among operating time, wear quantity of the piston and total acid number of the refrigerating machine oil with respect to each of different pistons according to an embodiment;

FIG. 6 is a chart showing characteristic correlations of wear quantity of the piston and total acid number of the refrigerating machine oil against surface hardness of the piston according to an embodiment;

FIG. 7 is a longitudinal sectional view of a rotary compressor according to a prior art;

FIG. 8 is a cross-sectional view of the rotary compressor according to a prior art; and

FIG. 9 is a configurational view of a refrigerating cycle apparatus according to a prior art.

DESCRIPTION OF EMBODIMENTS

In one aspect, A compressor for use in a refrigerating cycle apparatus, wherein a single refrigerant of hydrofluoroolefin having a double bond of carbon or a mixed refrigerant containing the hydrofluoroolefin and hydrofluorocarbon having no double bond of carbon is used, and a refrigerating machine oil containing an additive for suppressing deterioration of the refrigerating machine oil and an antiwear agent is used, the compressor including a sliding portion which is exposed to the mixed refrigerant and the refrigerating machine oil and which has a hardness of 47-55 HRC (Rockwell Hardness C-Scale). According to this compressor, decomposition and polymerization of the refrigerant and the refrigerating machine oil is inhibited, so that occurrence of sludge is inhibited. Also, antiwear property of sliding portions, e.g. piston and vane to be put into mutual sliding contact, of the compressor can be maintained. As a result, reliability of the compressor can be ensured.

The vane may be made from an iron-related material and subjected to nitriding treatment or may be made from a sintered alloy steel and subjected to sintering treatment and quenching treatment. When the vane is made from an iron-related material and subjected to nitriding treatment, the vane can be manufactured with low cost. As a result, the compressor can be mass produced. Also, when the vane is made from a sintered alloy steel and subjected to sintering treatment and quenching treatment, a hard structure with W, Mo, Cr, V-related carbides dispersed in minute martensite structures can be obtained.

Preferably, the vane is made from a high-speed tool steel. In this case, a vane even more excellent in antiwear property can be obtained.

A ceramic coating may be applied to the vane. By the ceramic coating, temperature increases due to friction between the tip end portion of the vane and the outer peripheral surface of the piston can be suppressed, so that decomposition of the refrigerant can be inhibited. Also, the polarity of the tip end portion of the vane is held by the ceramic coating, by which an extreme-pressure layer (antiwear agent film) is formed on the surface of the tip end portion of the vane. Thus, abnormal wear of the vane can be inhibited.

By the ceramic coating, a surface of the vane may be coated with a nitride or carbide of Ti (titanium), V (vanadium), Ta (tantalum), W (tungsten) or Nb (niobium). As a result, the antiwear property of the vane is improved and moreover its sliding resistance is reduced. Thus, temperature increases due to friction can be suppressed, so that decomposition and polymerization of the refrigerant and the refrigerating machine oil can be inhibited.

Preferably, the ceramic coating of a tip end portion of the vane to be put into contact with the piston has a thickness of 5-15 μm. Thus, reliability of the tip end portion of the vane that is subject to sliding contact under severe sliding conditions can be ensured.

Preferably, the ceramic coating is applied to only the tip end portion of the vane. Since ceramic coating is applied only to the tip end portion of the vane that is subject to sliding contact under severe sliding conditions, coating cost can be reduced.

The vane may be made from a ceramic material. Thus, temperature increases due to friction between the tip end portion of the vane and the outer peripheral surface of the piston can be suppressed, so that decomposition of the refrigerant and the refrigerating machine oil can be inhibited. Also, the polarity of the tip end portion of the vane is held, by which an extreme-pressure layer (antiwear agent film) is formed on the surface of the tip end portion of the vane. Thus, abnormal wear of the vane can be inhibited.

The piston may be made from cast iron. Since the piston is made from cast iron, surface hardness can be increased effectively by quenching and tempering and moreover carbon contained in the cast iron functions as a solid lubricant in sliding contact. Thus, the antiwear property of the piston is improved and moreover temperature increases due to friction can be suppressed, so that decomposition and polymerization of the refrigerant and the refrigerating machine oil is inhibited. That is, occurrence of sludge can be inhibited. Also, the use of cast iron allows the piston to be made with low cost. As a result, the compressor can be mass produced.

Preferably, cast iron, from which the piston is made, contains 0.4-1.2 wt % of chromium and 0.15-0.7 wt % of molybdenum. As a result of this, carbides in the cast iron are stabilized, so that the cast iron becomes densified in its structure, being improved in mechanical properties. Also, the sliding surface of the piston can be finished effectively into a desired surface configuration.

Preferably, the cast iron, from which the piston is made, contains 0.15-0.4 wt % of nickel. As a result of this, coarsening of graphite is inhibited, so that the cast iron can be densified in structure, being improved in mechanical properties. Also, the sliding surface of the piston can be finished effectively into a desired surface configuration. Further, graphitization is accelerated, by which chilling is inhibited, with the result that successful machinability can be obtained. As a consequence, productivity of the piston, i.e. productivity of the compressor, is improved.

Preferably, a surface of the vane and a surface of the piston have surface roughnesses of 0.4 μm Ra or less. As a result of this, the conforming period between the vane surface and the piston surface is shortened, so that a uniform extreme-pressure layer (antiwear agent film) is formed earlier on the surface. That is, the period of a high-temperature state, in which decomposition and polymerization of the refrigerant and the refrigerating machine oil are more likely to occur, is shortened. As a consequence, occurrence of sludge can be inhibited.

The refrigerant may be a refrigerant contains at least one of tetrafluoropropene or trifluoropropene, which is a kind of hydrofluoroolefin, and has a global warming potential within a range of 5 to 750, desirably 5 to 350. With such a refrigerant, it becomes implementable to provide a compressor of smaller environmental loads.

The refrigerant may be a refrigerant contains, as a principal ingredient, tetrafluoropropene or trifluoropropene, which is a kind of hydrofluoroolefin, and difluoromethane and pentafluoroethane are mixed in the refrigerant so that its global warming potential falls within a range of 5 to 750, desirably 5 to 350. With such a refrigerant, it becomes implementable to provide a compressor of smaller environmental loads.

The refrigerating machine oil may include (1) polyoxyalkylene glycols, (2) polyvinyl ethers, (3) poly(oxy)alkylene glycol or copolymers of its monoether and polyvinyl ether, (4) oxygenated compounds of polyol esters and polycarbonates, (5) a synthetic oil having a principal ingredient of alkylbenzenes or (6) a synthetic oil having a principal ingredient of α-olefins. With such a refrigerating machine oil, decomposition and polymerization of the refrigerant and the refrigerating machine oil is inhibited, so that occurrence of sludge is inhibited. Also, antiwear property of sliding portions, e.g. piston and vane to be put into mutual sliding contact, of the compressor can be maintained. As a result, reliability of the compressor can be ensured.

In another aspect, a refrigerating cycle apparatus comprises

the compressor as mentioned above, a condenser, an expansion mechanism and an evaporator, whereby a refrigerating cycle for compressing, condensing, expanding and evaporating the refrigerant is constituted. With such a refrigerating cycle apparatus, decomposition and polymerization of the refrigerant and the refrigerating machine oil is inhibited, so that occurrence of sludge is inhibited. Also, antiwear property of sliding portions, e.g. piston and vane to be put into mutual sliding contact, of the compressor can be maintained. As a result, reliability of the refrigerating cycle apparatus can be ensured.

Hereinbelow, an embodiment of the present invention will be described with reference to the accompanying drawings. It is noted that the invention is not limited by the following embodiment.

Embodiment

FIG. 1 shows a basic refrigerating cycle apparatus according to an embodiment of the invention. This refrigerating cycle apparatus, as shown in FIG. 1, has a compressor 120. The compressor 120 compresses a low-temperature, low-pressure refrigerant gas and discharges out a high-temperature, high-pressure refrigerant gas toward a condenser 121. The refrigerant gas fed to the condenser 121, while releasing its heat into the air, becomes a high-temperature, high-pressure refrigerant liquid, thus being fed to an expansion mechanism (e.g., expansion valve or capillary tube) 122. The high-temperature, high-pressure refrigerant liquid passing through the expansion mechanism 122 is transformed into a low-temperature, low-pressure wet steam by a restriction effect, thus being fed to an evaporator 123. The refrigerant having entered into the evaporator 123 absorbs heat from vicinities, evaporating. Then, the refrigerant gas coming out from the evaporator 123 is sucked into the rotary compressor 120. Such a cycle as shown above is repeated.

The compressor 120 to be used in such a refrigerating cycle apparatus as described above is shown in FIGS. 2 and 3. The compressor 120 shown in FIGS. 2 and 3 is a rotary compressor. This rotary compressor 120 has a stator 102 a of a motor 102 fixed at an upper portion of a closed container 101. Also, a compression mechanism section 105 having a shaft 104 driven by a rotor 102 b of the motor 102 is fixed at an upper portion of the closed container 101. A bearing 107 is fixed at an upper end of a cylinder 106 of the compression mechanism section 105, and a bearing 108 is fixed at a lower end thereof, with a bolt or the like. A piston 109 is placed in the cylinder 106. An eccentric portion 104 a of the shaft 104 is inserted into the piston 109 so that the piston 109 is eccentrically rotated by the eccentric portion 104 a. A vane 110 is inserted into a vane groove 106 a of the cylinder 106, and a vane spring 111 is placed at a rear portion 110 b of the vane 110. This vane spring 111 biases the vane 110 so that a tip end portion 110 a of the vane 110 is kept in contact with an outer peripheral surface of the piston 109.

Within the refrigerating cycle apparatus including the compressor 120, tetrafluoropropene (hereinafter, referred to as ‘HFO1234yf refrigerant’), which is a kind of hydrofluoroolefin having a double bond of carbon, is enclosed. Also, at a bottom portion of the closed container 101, refrigerating machine oil 103 containing base oil compatible with the HFO1234yf refrigerant is stored. Refrigerating machine oils 103 containing, as a principal ingredient, at least one kind of base oil of polyol ester, polyvinyl ether and polyalkylene glycol, may be used. In this embodiment, a refrigerating machine oil 103 whose principal ingredient is polyol ester alone is used.

The polyol ester-based refrigerating machine oil 103 is synthesized by dehydration reaction of polyhydric alcohol and saturated or unsaturated fatty acid. As the polyhydric alcohol that contributes to viscosity of the refrigerating machine oil 103, neopentyl glycol, pentaerythritol, dipentaerythritol or the like is used. As the saturated fatty acid, straight-chain fatty acids such as hexanoic acid, heptanoic acid, nonanoic acid, and decanoic acid as well as branched-chain fatty acids such as 2-methylhexanoic acid, 2-ethylhexanoic acid, and 3,5,5-trimethylhexanoic acid are used. It should be noticed that polyol ester oils containing a straight-chain fatty acid are good in sliding characteristic but inferior in hydrolyzability while ester oils containing a branched-chain fatty acid are slightly inferior in sliding characteristic but low in hydrolyzability, as their features.

Added to the refrigerating machine oil 103 of this embodiment are a sulfuric extreme-pressure additive for preventing wear and an additive for suppressing deterioration of the refrigerating machine oil. As the additive for suppressing deterioration of the refrigerating machine oil, various kinds of additives exemplified by antioxidants such as dibutyl-p-cresol, acid scavengers such as epoxy-containing compounds, metal deactivators, and antifoaming agents are selectively added to the refrigerating machine oil 103.

As the sulfuric extreme-pressure additive for preventing wear, there may be mentioned sulfurized oils and fats, sulfurized fatty acids, sulfurized esters, sulfurized olefins, dialkylpolysulfide, dibenzyldisulfide, oligomer polysulfide, and the like. Preferably, the number of sulfur bridges of these sulfuric extreme-pressure additives is 3 or less. If the sulfur bridge length is 4 or more, sulfur is more likely to be released into the refrigerating machine oil 103, so that copper used for piping or the like in the refrigerating cycle may be corroded.

Also, some of metal deactivators have a function of preventing corrosion of copper piping due to sulfur, and benzotriazoles can be used as such metal deactivators. Phosphorus-related extreme-pressure additives may also be used in order to improve the extreme-pressure effect. Usable as the phosphorus-related extreme-pressure additive are, for example, phosphate esters such as tricresyl phosphate and triphenyl phosphate, phosphite esters, and amine salts of acidic phosphate esters. Preferably, acidic phosphate esters such as tricresyl phosphate and triphenyl phosphate, which are superior in compatibility with the refrigerating machine oil 103 are favorable. Phosphorus-related extreme-pressure additives are higher in antiwear effect under low loads, as compared with sulfuric extreme-pressure additive. Therefore, combinational use of sulfuric extreme-pressure additives and phosphorus-related extreme-pressure additives is most suitable for compressors of refrigerating cycle apparatuses operated over wide frequency ranges by inverter control.

As described above, in the rotary compressor 120 of this embodiment, the piston 109, while eccentrically rotating within the cylinder 106, presses the tip end portion 110 a of the vane 110, by which the refrigerant is sucked in, compressed and discharged out. Therefore, the tip end portion 110 a of the vane 110 serving as a sliding portion, on which a coating film is formed, has a higher hardness as compared with portions other than the tip end portion 110 a of the vane 110. More specifically, as the coating film, CrN (chromium nitride), DLC (Diamond-Like Carbon), TiN (titanium nitride), and the like may be used. The coating film of the tip end portion 110 a of the vane 110 has a polarity holding effect and is formed by, for example, distribution of graphite or the like having benzene rings in connection. Along with approach of the refrigerating machine oil 103, there arises polarization at the coating film due to induction by the polarity of the refrigerating machine oil 103, so that the coating film comes to have a polarity. As a result, the extreme-pressure additive in the refrigerating machine oil 103 is adsorbed up, by which a extreme-pressure layer (extreme-pressure additive layer) is formed on the coating film. By the extreme-pressure layer formed at the sliding portion as shown above, even under a severe sliding condition (e.g., in a case where a full-power operation of the compressor is started after being left for half a day at outside air temperatures of −10° C. or lower), there never occurs lacks of lubricating oil at the sliding portions, so that abnormal wear of the sliding portions is inhibited.

With regard to the refrigerating cycle apparatus and the rotary compressor made up as described above, their operation and function will be described below with reference to FIGS. 2 and 3.

First, a refrigerant (HFO1234yf refrigerant) is sucked into a suction chamber 113 via a suction port 112 provided in the cylinder 106. Also, a refrigerant in a compression chamber 114 constituted by the vane 110, the piston 109 and the cylinder 106 is compressed by counterclockwise rotation (in arrow direction) of the piston 109, passing through a discharge cutout 115 so as to be discharged out via a discharge port (not shown) into the closed container 101. The compressed refrigerant discharged into the closed container 101 passes through the opening of the motor 102, being discharged out into the refrigerating cycle via a discharge pipe 116 placed at an upper portion of the closed container 101. In this process, mist of the refrigerating machine oil 103 present in vicinities is discharged out together. Then, the refrigerant discharged out into the refrigerating cycle passes through the condenser 121, the expansion mechanism 122 and the evaporator 123 in order as described above, being sucked again into the suction chamber 113 via the suction port 112 of the compressor.

In this case, the tip end portion 110 a of the vane 110 and the outer peripheral surfaces of the piston 109 in contact with each other are the sliding portions under the most severe sliding condition in the construction of the rotary compressor 120. Since a biasing force of the vane spring 111 as well as a high discharge pressure act on the rear portion 110 b of the vane 110, a large force corresponding to a differential pressure from a pressure inside the cylinder 106 acts on the vane 110, so that the region between the tip end portion 110 a of the vane 110 and the outer peripheral surface of the piston 109 results in a state of mixed lubrication or boundary lubrication.

From such a viewpoint as shown above, in this embodiment, the vane 110 is made from SKH, SKD, SUS, SCM or other like steel, and further nitrided. Moreover, on the surface of the tip end portion 110 a of the vane 110, a coating film of CrN or DLC or other ceramics is formed by PVD process. Thus, the surface of the tip end portion 110 a of the vane 110 has a hardness of about HV 1500-2000 and a surface roughness of about 0.2 μm tip-end Ra.

On the other hand, the piston 109 is made from cast iron containing 0.7-1.0 wt % of chromium (Cr), 0.2-0.4 wt % of molybdenum (Mo), and 0.2-0.4 wt % of nickel (Ni) (hereinafter, referred to as ‘Mo—Ni—Cr cast iron’), and subjected to quenching, subzero treatment, tempering, radiational cooling and the like so as to have a surface hardness of around 47-55 HRC. The reason for the surface hardness of 47-55 HRC will be described later. Also, since minute dent portions are present on the outer peripheral surface of the piston 109, which is a sliding surface, flat portions of the outer peripheral surface of the piston 109 except the minute dent portions are finished so as to have a surface roughness of about 0.2 μm Ra.

Next, an example of results obtained by performing real-machine operation tests with a refrigerating cycle apparatus in which the rotary compressor 120 was incorporated will be described below.

The vane 110 used in the tests was made from high-speed tool steel (SKH51), and on its tip end portion 110 a, a CrN ceramic coating film having a surface hardness of about HV1800, a film thickness of 5 μm and a surface roughness of 0.2 μm Ra was formed on the surface. The piston 109 used in the tests was made from Mo—Ni—Cr cast iron containing 0.7-1.0 wt % of chromium (Cr), 0.2-0.4 wt % of molybdenum (Mo), and 0.2-0.4 wt % of nickel (Ni), and has a surface hardness of about 50 HRC. A HFO1234yf refrigerant was used for the tests. On the other hand, the refrigerating machine oil 103 was prepared in plural kinds. More specifically, a refrigerating machine oil of Comparative Example 1, which was polyol ester alone, a refrigerating machine oil of Comparative Example 2, which was polyol ester containing an acid scavenger, and a refrigerating machine oil of Example 1, which was polyol ester containing an acid scavenger and an antiwear agent, were prepared. Three rotary compressors 120 were prepared for each of Comparative Example 1, Comparative Example 2 and Example 1. For each of Comparative Example 1, Comparative Example 2 and Example 1, overload operation tests were performed for 300 hours with a first rotary compressor 120, for 1000 hours with a second rotary compressor 120, and for 2000 hours with a third rotary compressor 120. After completion of the tests, wear quantity of the piston 109 and total acid number of the refrigerating machine oil 103 were measured with respect to each of the rotary compressors 120.

The total acid number is a number of milligrams (mg) of potassium hydroxide needed to neutralize all acidic ingredients contained in 1 g of a sample. The acid number is an index which is widely used for knowledge of a degree of oxidation of lubricating oil during its use or for evaluation of oxidation tests and service tests of lubricating oil after those tests, or the like. In this case, the total acid number corresponds to a generation quantity of hydrofluoric acid, which is a decomposition product of the refrigerant, and a generation quantity of carboxylic acid, which is a decomposition product of the refrigerating machine oil 103. Still more, the total acid number corresponds also to a quantity of sludge generated from decomposition and polymerization of the refrigerant and the refrigerating machine oil.

FIGS. 4( a) and 4(b) show characteristic correlations among operating time, wear quantity of the piston and total acid number of the refrigerating machine oil with respect to each of Example 1, Comparative Example 1 and Comparative Example 2. The horizontal axis represents operating time while the vertical axis of FIG. 4( a) represents wear quantity of the piston and the vertical axis of FIG. 4( b) represents total acid number.

As shown in FIG. 4( b), in the case of the refrigerating machine oil 103 of Comparative Example 1, which is polyol ester alone, an abrupt increase in acid value was confirmed. The reason of this can be deduced that the HFO1234yf refrigerant (a refrigerant composed principally of hydrofluoroolefin having a double bond of carbon), being lower in stability than HFC refrigerants, is easy to decompose and an acid generated by its decomposition accelerated deterioration of the refrigerating machine oil.

As a countermeasure for this, an acid scavenger was added to polyol ester, i.e., in the case of the refrigerating machine oil of Comparative Example 2, increases in the acid value were suppressed. However, as shown in FIG. 4( a), Comparative Example 2 showed increases in wear quantity, as compared with Comparative Example 1 using polyol ester alone. The reason of this can be deduced that with an oxidizer added to polyol ester as in Comparative Example 2, increases in acid value of the refrigerating machine oil can be inhibited by the acid scavenger, but meanwhile generation of fluoric reaction products that are decomposition products of the refrigerant is also inhibited. It can be inferred that the fluoric reaction products stick to the sliding portions of the compressor to serve as a solid lubricant that exerts an effect of reducing wear of the sliding portions.

On the other hand, it has been found from the result of Example 1 that with an acid scavenger and an antiwear agent added to polyol ester, increases in acid value of the refrigerating machine oil is inhibited by the acid scavenger (i.e., deterioration of the refrigerating machine oil is suppressed) and moreover wear quantity of the sliding portions is reduced by the antiwear agent.

Next, a further test using a plurality of different pistons 109 will be described.

Details of the pistons 109 of Example 2, Comparative Example 3 and Comparative Example 4 used in the test are shown in Table 1. The refrigerant used in the test is HFO1234yf refrigerant. In the test, the refrigerating machine oil 103, being polyol ester alone, was used in order to exclude effects of the refrigerating machine oil 103. With regard to test results, a similar tendency can be recognized also in cases where various additives are added to the refrigerating machine oil 103.

TABLE 1 Piston Vane Refrigerating Base Ingredients Hardness Base Hardness machine (material) Cr Mo Ni HRC (material) Coating HAVE oil Ex. 2 Mo—Ni—Cr 0.7-1.0 0.2-0.4 0.2-0.4 50 SKH CrN 1800 ester cast iron Comp. Mo—Ni—Cr 0.7-1.0 0.2-0.4 0.2-0.4 59 SKH CrN 1800 ester Ex. 3 cast iron Comp. Mo—Ni—Cr 0.7-1.0 0.2-0.4 0.2-0.4 41 SKH CrN 1800 ester Ex. 4 cast iron

The piston 109 of Example 2 is the same as the one explained with reference to FIGS. 2 and 3. The piston 109 of Example 2 is made from Mo—Ni—Cr cast iron containing 0.7-1.0 wt % of chromium (Cr), 0.2-0.4 wt % of molybdenum (Mo), and 0.2-0.4 wt % of nickel (Ni), and has a surface hardness of about 50 HRC. Also, the outer peripheral surface of the piston 109 is finished so that its flat portion except minute dent portions has a surface roughness of about 0.2 μm Ra.

The piston 109 of Comparative Example 3, although similar in material to Example 2, yet has a surface hardness of 59 HRC unlike Example 2. Also, the surface roughness is about 0.2 μm Ra.

The piston 109 of Comparative Example 4 is similar in material to Embodiment 2 and has a surface hardness of about 41 HRC. Also, the surface roughness is about 0.2 μm Ra.

FIG. 5( a) and FIG. 5( b) show characteristic correlations among operating time, wear quantity of the piston and total acid number of the refrigerating machine oil with respect to each of Example 2, Comparative Example 3 and Comparative Example 4. The horizontal axis represents operating time while the vertical axis of FIG. 5( a) represents wear quantity of the piston and the vertical axis of FIG. 5( b) represents total acid number.

First, wear quantity of the piston 109 shown in FIG. 5( a) is explained.

In any one of Example 2, Comparative Example 3 and Comparative Example 4, there is shown a tendency that progress of wear goes on faster in early stages and the progress of wear becomes slower with elapses of the operating time. As shown in FIG. 5( a), in general, wear in fast-wear regions (larger-gradient regions) is called initial wear, and wear in smaller-gradient regions is called steady wear. The initial wear, corresponding to a period in which minute bumps present on surfaces collide with one another so as to disappear, is also called conforming process. After an end of the conforming process, the surface become smoother to some extent, where the surface pressure lowers locally so that the progress of wear becomes slower.

As shown in FIG. 5( a), there is a tendency that the initial wear period of Comparative Example 4, having the lowest surface hardness of the piston 109, is relatively shorter while the initial wear period of Comparative Example 3, having the highest surface hardness, is relatively longer.

In addition, FIG. 5( a) also shows, in dotted line, an upper-limit value of the wear quantity of the piston resulting after a 2000-hour overload operation of a compressor as a prior art example in which an HFC refrigerant is used, the compressor including the same vane 110 and a piston 109 having a surface hardness of 40-60 HRC (a range of primary use with the use of an HFC refrigerant).

As shown in FIG. 5( a), all of Example 2, Comparative Example 3 and Comparative Example 4 are generally equivalent in wear quantity to the prior art example (a case with use of an HFC refrigerant). The wear quantity of the piston 109 of Comparative Example 4, having the lowest surface hardness, is relatively large, while the wear quantity of Example 2 and the wear quantity of Comparative Example 3, having the highest surface hardness, are at generally equal level.

Next, characteristics of total acid number of the refrigerating machine oil as shown in FIG. 5( b) will be explained.

In addition, FIG. 5( b) also shows, in dotted line, an upper-limit value of the total acid number of the refrigerating machine oil resulting after a 2000-hour overload operation of a compressor as a prior art example in which an HFC refrigerant is used, the compressor including the same vane 110 and a piston 109 having a surface hardness of 40-60 HRC (a range of primary use with the use of an HFC refrigerant).

All of Example 2, Comparative Example 3 and Comparative Example 4 show a tendency that the increasing speed of total acid number is higher in early stages and the increasing speed of total acid number becomes lower with elapsing time.

Comparative Example 3, having the highest surface hardness of the piston 109, shows the largest increment in total acid number such that the total acid number of Comparative Example 3 becomes higher in value than the total acid number of the prior art example (a case using an HFC refrigerant). Also, Comparative Example 4, having the lowest surface hardness of the piston 109, finally results in a higher value as compared with the prior art example. Meanwhile, Example 2 finally results in a total acid number generally equal to that of the prior art example.

Considerations as to characteristic correlations among operating time, wear quantity of the piston 109 and total acid number will be given below.

The difference in total acid number between Example 2 and Comparative Example 3 can be considered attributable to the hardness of the piston 109. Generally, local temperature increases in the sliding portions are caused by contact among minute bumps present on individual sliding surfaces of mutual sliding, where the degree of temperature increases, it is said, is inversely proportional to radii of contact points of the minute bumps. With an excessively high surface hardness of the piston 109 relative to the CrN-ceramic coated vane 110, the surface of the piston 109 and the surface of the vane 110 become less likely to meet each other, i.e., the minute bumps of the piston 109 are less likely to disappear, so that radii of contact points of the minute bumps present in the surface of the piston 109 are kept remaining small. Thus, the region between the vane 110 and the piston 109 is kept in a locally high-temperature state. Also, with reference to FIG. 5( a) and FIG. 5( b), an initial wear period (i.e., a period until minute bumps disappear) and a period of high increasing speed of the total acid number are generally coincident with each other. In other words, a period in which the region between the vane 110 and the piston 109 is kept in a locally high-temperature state and a period in which the increasing speed of the total acid number keeps high are generally coincident with each other. From this finding, it can be inferred that decomposition of the HFO1234yf refrigerant having a double bond of carbon, which is lower in stability than HFC refrigerants of conventional use was accelerated by heat generated in the region between the vane 110 and the piston 109 during the initial wear period. Then, it can be inferred that hydrogen fluoride (hydrofluoric acid) was generated by decomposition of the HFO1234yf refrigerant and the generated hydrogen fluoride contributed to decomposition of the refrigerating machine oil 103 (generation of carboxylic acid or the like), which was reflected to changes in the total acid number. Therefore, in order to suppress increases in total acid number, there is a need for setting a proper difference in surface hardness between the vane 110 and the piston 109, i.e., setting a proper upper-limit value of surface hardness of the piston 109, so that the initial wear is ended earlier, prompting an earlier move to steady wear, which is a state that the surface pressure is locally lowered.

On the other hand, as shown in FIG. 5( b), the cause that Comparative Example 4, having the lowest surface hardness of the piston 109, is higher in total acid number than the prior art example as is the case also with Comparative Example 3 having the highest hardness of the piston 109 can be deduced as described below.

Comparative Example 4 involves high wear quantity of the piston. Discharged abrasion powder, which is much activated, is considered as serving as a catalyst that accelerates the decomposition of the HFO1234yf refrigerant. For this reason, it can be inferred that the total acid number of Comparative Example 4, involving generation of the most abrasion powder, became higher than that of the prior art example, i.e., a case with use of an HFC refrigerant. Accordingly, there is a need for securing antiwear property by properly setting a difference in surface hardness between the vane 110 and the piston 109, i.e., properly setting a lower-limit value of the surface hardness of the piston 109.

FIG. 6( a) and FIG. 6( b) show characteristic correlations among wear quantity of the piston and total acid number of the refrigerating machine oil against the surface hardness of the piston. Characteristic correlations shown in the figure were obtained by the following test. The vane 110 used in the test was made from a high-speed tool steel (SKH51) and coated with a CrN ceramic coating film having a surface hardness of about 1800 HV, a film thickness of 5 μm and a surface roughness of 0.2 μm Ra. The refrigerant used in the test was a HFO1234yf refrigerant. The refrigerating machine oil 103 was polyol ester. A plurality of rotary compressors 120 having pistons 109 different in surface hardness from one another and having a surface roughness of about 0.2 μm Ra and made from Mo—Ni—Cr cast iron were prepared. Then, the individual compressors were subjected to a 1000-hour overload operation. After completion of the test, wear quantity of the piston 109 and total acid number of the refrigerating machine oil 103 were measured with each of the rotary compressors 120.

The horizontal axis represents hardness of the piston 109 while the vertical axis of FIG. 6( a) represents wear quantity of the piston and the vertical axis of FIG. 6( b) represents total acid number.

As shown in FIG. 6, it can be understood that with use of the HFO1234yf refrigerant and with the surface hardness of the piston 109 falling within a range of 47-55 HRC, wear quantity of the piston and total acid number equivalent to those of the prior art example (a case with use of a HFC refrigerant) can be ensured.

From the results described above, by using a refrigerant containing hydrofluoroolefin having a double bond of carbon, by using polyol ester containing an acid scavenger and an antiwear agent as the refrigerating machine oil 103, by forming the vane 110 of the rotary compressor 120 from iron-related materials with ceramic coating provided thereon, and by setting the surface hardness of the piston 109 to 47-55 HRC, it becomes possible to inhibit decomposition and polymerization of the refrigerant and the refrigerating machine oil 103 (i.e., to inhibit occurrence of sludge) so that the antiwear property of the vane 110 and the piston 109 can be maintained. As a result, the reliability of the compressor 120 and the refrigerating cycle apparatus using the compressor can be ensured.

In addition, it is also allowable that hydrofluorocarbon (HFC32, HFC125), having no double bond, is mixed with tetrafluoropropene (HFO1234yf), which is the refrigerant of this embodiment. This mixed refrigerant, in spite of being a non-azeotropic refrigerant mixture, behaves in a generally same manner as pseudo-azeotropic mixed refrigerants of smaller boiling-point temperature differences. As a result, cooling performance and cooling coefficient of performance (COP) of the cooling cycle apparatus are improved. Although a single refrigerant, hydrofluoroolefin, is used in this embodiment, similar effects can be obtained even when a mixed refrigerant containing hydrofluoroolefin and hydrofluorocarbon is used.

Also in the case of a mixed refrigerant, its mixing ratio is preferably set so that the GWP value falls within a range of 5 to 750, desirably, 5 to 350. For example, in order that HFO1234yf and HFC32 are mixed together to obtain a GWP value of 350 or less, it is necessary that HFO1234yf occupies 56 wt % or more. Also, in order that HFO1234yf and HFC125 are mixed together to obtain a GWP value of 750 or less, it is necessary that HFO1234yf occupies 78.7 wt % or more, and for a GWP value of 350 or less, HFO1234yf needs to occupy 91.6 wt % or more. By doing so, effects of the refrigerant on global warming can be kept at a minimum.

Further, although polyol ester oil compatible with HFO1234yf is used as the refrigerating machine oil 103, it is also allowable to use polyvinyl ether or polyalkylene glycol having the compatibility as well as the refrigerating machine oil 103. Even with use of these refrigerating machine oils, the compressor 120 can recover these refrigerating machine oils, so that a compressor 120 of high reliability can be obtained as in the case of polyol ester oil. Besides, since these refrigerating machine oils have capability with the mixed refrigerant of HFO1234yf and HFC, similar effect as with polyol ester oil can be obtained.

The piston 109 of this embodiment is made from Mo—Ni—Cr cast iron containing 0.7-1.0 wt % of chromium (Cr), 0.2-0.4 wt % of molybdenum (Mo), and 0.2-0.4 wt % of nickel (Ni). However, similar effects can be obtained also with a piston 109 made from Mo—Ni—Cr cast iron containing 0.4-1.2 wt % of chromium, 0.15-0.7 wt % of molybdenum, and 0.15-0.4 wt % of nickel. Also, similar effects can be obtained also with use of a piston 109 made from cast iron containing no nickel (Mo—Cr cast iron).

Although cast iron material is used as the material for making the piston 109 of this embodiment, iron-related materials containing chromium, molybdenum and nickel (e.g., carbon steel, tool steel, etc.) may also be used.

Although the surface roughness of the tip end portion 110 a of the vane 110 (surface roughness of the ceramic coating film) and the surface roughness of the piston 109 (flat portion except minute dent portions) are about 0.2 μm Ra in this embodiment, yet similar effects can be obtained also with their surface roughnesses of 0.4 μm Ra or less. With the surface roughness over 0.4 μm Ra, the tip end portion 110 a of the vane 110 and the outer peripheral surface of the piston 109 become less compatible with each other, so that an increase in total acid number may be incurred resultantly.

The invention has been described by taking a case the vane 110 and the piston 109 as an example, the invention is also applicable to other sliding portions of the compressor 120, for example, sliding portions of the shaft and the bearing. Moreover, the invention is not limited to rotary type compressors, and applicable to compressors such as scroll compressors. Scroll compressors have stationary-side and turning-side scrolls and the like as sliding portions.

Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are apparent to those skilled in the art. Such Changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart therefrom.

The entire disclosure of Japanese Patent Applications No. 2010-199604 filed on Sep. 7, 2010 and No. 2010-234329 filed on Oct. 19, 2010, including specification, claims, drawings, and summary are incorporated herein by reference in its entirety.

INDUSTRIAL APPLICABILITY

As described above, a compressor, as well as the refrigerating cycle apparatus using the compressor, according to the present invention are capable of ensuring the reliability of the compressor even with use of a mixed refrigerant of hydrofluoroolefin, having a double bond of carbon, and hydrofluorocarbon, having no double bond of carbon. Therefore, the invention is applicable also to compressors for hot-water supply devices, compressors for automotive air conditioners, compressors for refrigerator-freezers, compressors for dehumidifiers, and the like.

REFERENCE SIGNS LIST

-   103 refrigerating machine oil -   105 compression mechanism section -   106 cylinder -   109 piston -   110 vane -   120 compressor -   121 condenser -   122 expansion mechanism -   123 evaporator 

1. A compressor for use in a refrigerating cycle apparatus, wherein a single refrigerant of hydrofluoroolefin having a double bond of carbon or a mixed refrigerant containing the hydrofluoroolefin and hydrofluorocarbon having no double bond of carbon is used, and a refrigerating machine oil containing an additive for suppressing deterioration of the refrigerating machine oil and an antiwear agent is used, the compressor including a sliding portion which is exposed to the mixed refrigerant and the refrigerating machine oil and which has a hardness of 47-55 HRC.
 2. The compressor according to claim 1, including, as the sliding portions, a piston and a vane which are put into sliding contact with each other.
 3. The compressor according to claim 2, wherein the vane is made from an iron-related material and subjected to nitriding treatment or made from a sintered alloy steel and subjected to sintering treatment and quenching treatment.
 4. The compressor according to claim 3, wherein the iron-related material or the sintered alloy steel is a high-speed tool steel.
 5. The compressor according to claim 3, wherein ceramic coating is applied to the vane.
 6. The compressor according to claim 5, wherein by the ceramic coating, a surface of the vane is coated with a nitride or carbide of Ti (titanium), V (vanadium), Ta (tantalum), W (tungsten) or Nb (niobium).
 7. The compressor according to claim 5, wherein the ceramic coating of a tip end portion of the vane to be put into contact with the piston has a thickness of 5-15 μm.
 8. The compressor according to claim 5, wherein the ceramic coating is applied to only the tip end portion of the vane.
 9. The compressor according to claim 2, wherein the vane is made from a ceramic material.
 10. The compressor according to claim 2, wherein the piston is made from cast iron.
 11. The compressor according to claim 10, wherein the cast iron contains 0.4-1.2 wt % of chromium and 0.15-0.7 wt % of molybdenum.
 12. The compressor according to claim 11, wherein the cast iron contains 0.15-0.4 wt % of nickel.
 13. The compressor according to claim 2, wherein a surface of the vane and a surface of the piston have surface roughnesses of 0.4 μm Ra or less.
 14. The compressor according to claim 1, wherein the refrigerant contains at least one of tetrafluoropropene or trifluoropropene, which is a kind of hydrofluoroolefin, and has a global warming potential within a range of 5 to 750, desirably 5 to
 350. 15. The compressor according to claim 1, wherein the refrigerant contains, as a principal ingredient, tetrafluoropropene or trifluoropropene, which is a kind of hydrofluoroolefin, and difluoromethane and pentafluoroethane are mixed in the refrigerant so that its global warming potential falls within a range of 5 to 750, desirably 5 to
 350. 16. The compressor according to claim 1, wherein the refrigerating machine oil includes (1) polyoxyalkylene glycols, (2) polyvinyl ethers, (3) poly(oxy)alkylene glycol or copolymers of its monoether and polyvinyl ether, (4) oxygenated compounds of polyol esters and polycarbonates, (5) a synthetic oil having a principal ingredient of alkylbenzenes or (6) a synthetic oil having a principal ingredient of α-olefins.
 17. A refrigerating cycle apparatus comprising: the compressor according to claim 1; a condenser; an expansion mechanism; and an evaporator, whereby a refrigerating cycle for compressing, condensing, expanding and evaporating the refrigerant is constituted. 